Troubleshooting Trailer Taillights that Only Work with Headlights On

Question:

I purchased a set of your STL-78RB trailer lights, after wiring them they only work when the vehicle headlights are turned on. I checked my other trailers and they work fine, so I Am wondering if I wired them correctly. I matched the colors of the wires so it seems they should work.

asked by: Byron D

Expert Reply:

The first thing I would do is check to make sure the Rectangular Submersible LED Trailer Tail # STL16RB that you installed is grounded well. Ground issues can cause all sorts of bizarre behavior, and they tend to be at fault when lights only work when certain circuits are activated. You will want to make sure the white wire is grounded to a clean metal surface free of paint and rust. You also want to make sure the white wire of the 4-way on your trailer is grounded to a clean metal surface.

Now if that does not fix the problem you will want to use a circuit tester like our part # PTW2993 to verify the functions of the circuits you used to install this light. The circuit you attached green wire to should only see voltage when the brakes or right blinker is applied and the brown wire circuit should only see voltage when the running/head lights are on.

I attached an FAQ on trailer wiring for you to check out also.

expert reply by: Jameson C